Goniometer head for x-ray diffraction apparatus with improved z-motion mechanism

ABSTRACT

This disclosure depicts a goniometer head for securing and positioning a crystal specimen in X-ray diffraction apparatus. The disclosure stresses a lockable variable friction drive Z-axis translation mechanism for the head.

United States Patent Inventor Roy Leander Thomas, Jr.

Medway, Mass. App]. No. 843,541 Filed July 22, 1969 Patented Feb. [6, 1971 Assignee Charles Supper Co., Inc.

Natiek, Mass.

GONIOMETER HEAD FOR X-RAY DIFFRACTION APPARATUS WITH IMPROVED Z-MOTION MECHANISM 11 Claims, 3 Drawing Figs.

US. Cl. 250/51.5, 74/422, 269/59 Int. Cl G01n 23/20 [50] Field ofSearch 269/58, 59; 74/422; 250/515 References Cited OTHER REFERENCES Cullity; Elements of X-ray Diffraction; (1956); pp. 143, I44.

Primary Examiner-James W. Lawrence Assistant Examiner-A. L. Birch Att0rney-John H. Coult l I g p E llllllllllllllllllllu- PATENTED FEB] s IQYI- ROY L.THOMAS JR.

INVENTOR I GONIOMETER HEAD FOR X-RAY DIFFRACTION APPARATUS WITII IMPROVED Z-MOTION MECHANISM BACKGROUND OF THE INVENTION In X-ray diffraction analysis of crystals, it is of utmost importance that the crystalographer be able to fix the position and orientation of the crystal specimen with maximum precision and accuracy and that the crystal, once positioned, remains in the set position with minimum position drift or vibration. Goniometer heads which have been developed for securing and positioning crystals commonly provide 4 of crystal position adjustment, in addition to the azimuth adjustment capability usually incorporated in the goniometer head mount, namely, mutually orthogonal X and Y motions perpendicular to the axis of the head (the Z axis) and two orthogonal concentric arc motions. Certain goniometer heads provide a sixth degree of adjustment Z-motion, i.e. along the head axis.

The Z-motion mechanism ideally should have the following characteristics:

1. a positive, extremely precise adjustment action in both directions;

2. absence of any play or looseness in any of the remaining 5 of freedom; and 3. it should be capable of being locked securely in any position.

Prior art Z-motion mechanisms have fallen considerably short of satisfying the above list of desirable characteristics. 2- motion mechanisms in commercially available goniometer heads commonly have an undesirable amount of play, especially in azimuth. The most common types do not provide for locking of the Z-motion carriage and offer positive drive of the carriage in only one direction.

OBJECTS OF THE INVENTION It is an object of this invention to provide a goniometer head having a Z-motion mechanism which closely approaches meeting the above stated desirable characteristics. It is thus an object to provide a Z-motion mechanism which has a precise bidirectionally positive control, which exhibits very little transverse or azimuthal play, and which is fully lockable in any position.

Further objects and advantages of this invention will in part be obvious and will in part become apparent as the following description proceeds. The features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

DESCRIPTION OF THE DRAWINGS For a fuller understanding of the invention, reference may be had to the following detailed description taken in connection with accompanying drawings wherein:

FIG. I is a perspective view of a goniometer head having a Z-motion mechanism embodying the principles of the invention;

FIG. 2 is a view of FIG. 1 with the Z-motion mechanism exploded from the head;

FIG. 3 is a sectional view taken along lines 3-3 in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. l-3 illustrate a goniometer head including a Z- motion mechanism embodying the principles ofthe invention. The goniometer head 10 is of the eucentric type providing two orthogonal concentric arc motions and orthogonal X, Y and Z motions within the compass of the arcs. In the illustrated goniometer head 10 the arc motion mechanisms are conventional. The outside arc motion mechanism 11 comprises an outside arc carriage 12 traveling in an arcuate channel member 14, being adjustable in position by means of a rotatable screw 16 engaging threads (not shown) on the periphery of the carriage I2. Similarly, the inside arc motion mechanism 18, oriented at 90 to the outside arc motion mechanism 11, includes an inside arc carriage 20 which is supported for arcuate motion by an arcuate channel member 22, the carriage 20 being adjustable by means of a screw 24 engaging threads on the outer periphery of the carriage 20.

The X and Y-motion mechanisms in the head 10 embody another of my inventions which is unrelated to the subject invention. A housing 26 defines a pair of orthogonally arranged generally trapezoidal channels for receiving an X-motion carriage 28 driven by an X-adjustment screw 30 and a Y-motion carriage 32 driven by a Y-adjustment screw 33. Lock screws ,34 and 35 lock the X and Y-motion carriages, respectively.

This invention is directed to a novel Z-motion mechanism for providing a precise, bidirectionally positive and lockable Z-motion control of the crystal position. Referring now particularly to FIGS. 2 and 3, the Z-motion mechanism of this invention comprises a housing 36 defining an open-ended channel 38 for slidably receiving a Z-motion carriage 40. The carriage 40 includes a circular opening 42 at the outer end thereof within which a crystal-holding pin 44 may be received. A lock screw 46 is provided for locking the pin 44 in the opening 42. The lock screw 46 projects into an elongated slot 48 in the housing 36 to limit the extent of travel of the Z-motion carriage 40 in both directions.

Friction drive means for driving the Z-motion carriage 40 along the Z axis comprises a drive roller 50 loosely held for rotation in a bore 52 slightly elongated along the Y axis. The roller 50 is thus free to rotate and also to translate to a limited extend along the Y axis. The reason for the Y-axis freedom will become evident as this description proceeds. The carriage 40 has a rib 54 extending parallel to the Z axis which is received in an annular groove 56 in the center of the drive roller 50. See FIG. 3.

In order to maximize the frictional engagement of the groove 56 and the rib 54, the rib has tapered sides 58,60 which mate with sides 62,64 on the groove 56 having a like taper angle. It is evident that rotation of the drive roller will cause the Z-motion carriage to travel along the Z axis in a direction dependent upon the direction of rotation of the roller 50.

It is a stated object of this invention to provide a Z-motion mechanism having a very precise control and which is fully lockable in any position. Furthering this end, adjustable carriage loading means 66 are provided for placing a selectively variable compressive loading of the drive roller 50 against carriage 40. The carriage loading means 66 is illustrated as comprising a manually adjustable screw 68 received in an internally threaded bore 68 in the housing 36.

A pressure pad 72, which may be composed of nylon or the like, is received in the bore 70 in engagement with the drive roller 50. A compression spring 74, located in the bore 70 between the screw 68 and the pressure pad 72, exerts a force on the pad 72 dependent on the axial position of the screw 68 in the bore 70. By manually rotating the screw 68, the operator can select the desired frictional drive force exerted on the carriage 40 by the roller 50. Thus, the tightness of the action during operation of the Z-motion mechanism can be selectively controlled by the operator. Upon attaining the desired position of the crystal specimen along the Z-axis, the screw 68 is further rotated beyond a point wherein an extension 76 on the screw 68 engages the pad 72 directly and until the carriage 40 is frictionally locked in the channel 38.

The reason for the Y axis elongation of the bore 52 becomes evident from the above description the bore allows the freedom of motion of the roller 50 along the Y axis which is necessary to cover all ranges of frictional loading of the carriage and Y axis movement of the carriage 40 in channel 38.

In order to minimize play between the Z-motion carriage 40 and the channel 38 in the housing 36, the channel 38 is constructed to have a pair of planar walls convergent in the direction of the loading force applied by the carriage loading means 66. These walls receive mating surfaces on the carriage 40 having a similar tapered configuration. The illustrated arrangement may be described as a dovetail; however, other ar rangements utilizing the dovetail principle may be employed in order that the carriage will be self-locating and self-stabilizing in the channel 38.

A key feature of the described arrangement is the use of a self-locating and self-stabilizing carriage (through the taper or dovetail configuration) in combination with a rotary drive means (the roller 50) which follows the carriage as it moves in a plane perpendicular to the Z axis seeking its stable position. The roller is free to move in the direction along its own axis (here shown as being along the X axis), and also in the direction orthogonal thereto (along the Y axis). Further, the rib and groove engagement of the roller and carriage causes the following action to be extremely positive. The result is high precision at relatively low cost.

The invention is not limited to the embodiment depicted which is merely illustrative. It is contemplated that various and other modifications will occur to those skilled in the art.

lclaim:

1. In a goniometer head for X-ray diffraction apparatus having crystal position adjustment means providing two orthogonal translational crystal motions and two orthogonal arcuate crystal motions, a Z-motion mechanism for providing crystal position adjustment along the Z axis of the head, comprising:

carriage support means the Z axis;

Z-motion carriage means adapted to travel in said channel, said carriage means having a surface extending parallel to said Z axis;

friction drive means for driving said carriage means, said friction drive means having an annular area engaging said surface of said carriage means extending parallel to said Z axis;

means mounting said friction drive means for rotation; and

adjustable carriage loading means for placing a variable compressive loading of said friction drive means against said carriage means, whereby with a predetermined loading of said carriage means by said adjustable carriageloading means, rotation of said friction drive means causes said carriage means to translate along the Z axis.

2. The apparatus defined by claim 1 wherein said channel and said carriage means have operative mating surfaces comprising two intersecting planar surfaces arranged convergent away from the direction of said loading applied by said carriage-loading means against said carriage means, whereby said carriage means is self-locating and self-stabilizing in said channel.

3. The apparatus defined by claim 1 wherein said adjustable carriage-loading means comprises means defining an internally threaded bore, screw means in said bore, a pressure pad aligned with said bore and engaging said friction drive means, and compression spring means in said bore between said screw means and said pad, rotation of said screw means causing an adjustment of the loading applied by said pad upon said friction drive means.

4. The apparatus defined by claim 1 wherein said carriage surface extending parallel to said Z axis comprises a protruding rib with tapered sides, and wherein said friction drive means has an annular notch which receives said rib in driving engagement therewith, said notch having a cross section with tapered sides having a taper substantially mating with the taper on said rib.

5. The apparatus defined by claim 4 wherein said adjustable carriage-loading means comprises means defining an internally threaded bore, screw means in said bore, a pressure pad aligned with said bore and engaging said friction drive means, and compression spring means in said bore between said screw means and said pad, rotation of said screw means causing an defining a channel oriented along adjustment of the loading applied by said pad upon said friction drive means.

6. The apparatus defined by claim 5 wherein said channel and said carriage means have operative mating surfaces comprising two intersecting planar surfaces arranged convergent away from the direction of said loading applied by said carriage-loading means against said carriage means, whereby said carriage means is self-locating and self-stabilizing in said channel.

7. In a goniometer head for X-ray diffraction apparatus having crystal position adjustment means providing two orthogonal translational crystal motions and two orthogonal arcuate crystal motions, a Z-motion mechanism for providing crystal position adjustment along the Z axis of the head, compl'lSlIlgZ carriage support means defining a channel oriented along the Z axis;

Z-motion carriage means adapted to travel in said channel, said carriage having a surface extending parallel to said 2 axis, said channel and said carriage means having operative mating g'uide surfaces comprising two intersecting planar surfaces arranged convergent away from the direction of said loading applied by said carriage-loading means against said carriage means, whereby said carriage means is self-locating and self-stabilizing in said channel;

friction drive means for driving said carriage means, said friction drive means having an annular area engaging said surface of said carriage means extending parallel to said 2 axis;

mounting mearis mounting said friction drive means to rotate about an axis perpendicular to said Z axis and to float in a plane perpendicular to said Z axis, whereby said friction drive means is free to follow said carriage means as it locates its stable position in said channel; and

adjustable carriage-loading means for placing a variable compressive loading of said friction drive means against said carriage means, whereby with a predetermined loading of said carriage means by said adjustable carriageloading means, rotation of said friction drive means causes said carriage meansto translate along the Z axis.

8. The apparatus defined by claim 7 wherein said mounting means comprises a housing having a bore with a cross section elongated in a direction lying in said plane, and wherein said friction drive means comprises a manually rotatable roller loosely held in said bore.

9. The apparatus defined by claim 8 wherein said carriage surface extending parallel to said Z axis comprises a protruding rib with tapered sides, and wherein said friction drive means has an annular notch which receives said rib in driving engagement therewith, said notch having a cross section with tapered sides having a taper substantially mating with the taper on said rib.

10. The apparatus defined by claim 9 wherein said adjustable carriage-loading means comprises means defining an internally threaded bore, screw means in said bore, a pressure pad aligned with said bore and engaging said friction drive means, and compression spring means in said bore between said screw means and said pad, rotation of said screw means causing an adjustment of the loading applied by said pad upon said friction drive means.

11. In a goniometer head for X-ray diffraction apparatus, a mechanism for providing crystal position adjustment along a predetermined axis of the head, comprising:

carriage support means defining a channel oriented along said axis;

carriage means adapted to travel in said channel, said carriage means having a surface extending parallel to said axis;

drive means for driving carriage means, said drive means having a peripheral area engaging said surface of said carriage means extending parallel to said axis;

means loosely mounting said drive means for rotation; and

adjustable carriage-loading means for placing a variable loading of said drive means against said carriage means, thereby with a predetermined loading of said carriage means by said adjustable carriage-loading means, rotation of said drive means causes said carriage means to translate along said axis. 

1. In a goniometer head for X-ray diffraction apparatus having crystal position adjustment means providing two orthogonal translational crystal motions and two orthogonal arcuate crystal motions, a Z-motion mechanism for providing crystal position adjustment along the Z axis of the head, comprising: carriage support means defining a channel oriented along the Z axis; Z-motion carriage means adapted to travel in said channel, said carriage means having a surface extending parallel to said Z axis; friction drive means for driving said carriage means, said friction drive means having an annular area engaging said surface of said carriage means extending parallel to said Z axis; means mounting said friction drive means for rotation; and adjustable carriage loading means for placing a variable compressive loading of said friction drive means against said carriage means, whereby with a predetermined loading of said carriage means by said adjustable carriage-loading means, rotation of said friction drive means causes said carriage means to translate along the Z axis.
 2. The apparatus defined by claim 1 wherein said channel and said carriage means have operative mating surfaces comprising two intersecting planar surfaces arranged convergent away from the direction of said loading applied by said carriage-loading means against said carriage means, whereby said carriage means is self-locating and self-stabilizing in said channel.
 3. The apparatus defined by claim 1 wherein said adjustable carriage-loading means comprises means defining an internally threaded bore, screw means in said bore, a pressure pad aligned with said bore and engaging said friction drive means, and compression spring means in said bore between said screw means and said pad, rotation of said screw means causing an adjustment of the loading applied by said pad upon said friction drive means.
 4. The apparatus defined by claim 1 wherein said carriage surface extending parallel to said Z axis comprises a protruding rib with tapered sides, and wherein said friction drive means has an annular notch which receives said rib in driving engagement therewith, said notch having a cross section with tapered sides having a taper substantially mating with the taper on said rib.
 5. The apparatus defined by claim 4 wherein said adjustable caRriage-loading means comprises means defining an internally threaded bore, screw means in said bore, a pressure pad aligned with said bore and engaging said friction drive means, and compression spring means in said bore between said screw means and said pad, rotation of said screw means causing an adjustment of the loading applied by said pad upon said friction drive means.
 6. The apparatus defined by claim 5 wherein said channel and said carriage means have operative mating surfaces comprising two intersecting planar surfaces arranged convergent away from the direction of said loading applied by said carriage-loading means against said carriage means, whereby said carriage means is self-locating and self-stabilizing in said channel.
 7. In a goniometer head for X-ray diffraction apparatus having crystal position adjustment means providing two orthogonal translational crystal motions and two orthogonal arcuate crystal motions, a Z-motion mechanism for providing crystal position adjustment along the Z axis of the head, comprising: carriage support means defining a channel oriented along the Z axis; Z-motion carriage means adapted to travel in said channel, said carriage having a surface extending parallel to said Z axis, said channel and said carriage means having operative mating guide surfaces comprising two intersecting planar surfaces arranged convergent away from the direction of said loading applied by said carriage-loading means against said carriage means, whereby said carriage means is self-locating and self-stabilizing in said channel; friction drive means for driving said carriage means, said friction drive means having an annular area engaging said surface of said carriage means extending parallel to said Z axis; mounting means mounting said friction drive means to rotate about an axis perpendicular to said Z axis and to float in a plane perpendicular to said Z axis, whereby said friction drive means is free to follow said carriage means as it locates its stable position in said channel; and adjustable carriage-loading means for placing a variable compressive loading of said friction drive means against said carriage means, whereby with a predetermined loading of said carriage means by said adjustable carriage-loading means, rotation of said friction drive means causes said carriage means to translate along the Z axis.
 8. The apparatus defined by claim 7 wherein said mounting means comprises a housing having a bore with a cross section elongated in a direction lying in said plane, and wherein said friction drive means comprises a manually rotatable roller loosely held in said bore.
 9. The apparatus defined by claim 8 wherein said carriage surface extending parallel to said Z axis comprises a protruding rib with tapered sides, and wherein said friction drive means has an annular notch which receives said rib in driving engagement therewith, said notch having a cross section with tapered sides having a taper substantially mating with the taper on said rib.
 10. The apparatus defined by claim 9 wherein said adjustable carriage-loading means comprises means defining an internally threaded bore, screw means in said bore, a pressure pad aligned with said bore and engaging said friction drive means, and compression spring means in said bore between said screw means and said pad, rotation of said screw means causing an adjustment of the loading applied by said pad upon said friction drive means.
 11. In a goniometer head for X-ray diffraction apparatus, a mechanism for providing crystal position adjustment along a predetermined axis of the head, comprising: carriage support means defining a channel oriented along said axis; carriage means adapted to travel in said channel, said carriage means having a surface extending parallel to said axis; drive means for driving carriage means, said drive means having a peripheral area engaging said surface of said carriage means extending parallel to said Axis; means loosely mounting said drive means for rotation; and adjustable carriage-loading means for placing a variable loading of said drive means against said carriage means, thereby with a predetermined loading of said carriage means by said adjustable carriage-loading means, rotation of said drive means causes said carriage means to translate along said axis. 